1. Technical Field
The present invention relates to a piston designed for reciprocating movement in a cylinder in an internal combustion engine. More specifically, the present invention relates to a piston having a lateral surface that is provided with at least two spaced peripheral piston ring grooves for individual piston rings.
2. Background Information
It is known that it is not possible in an internal combustion engine to provide piston ring sealing between pistons and their surrounding cylinder walls that completely seals off the combustion chambers from the crankcase of the engine. A certain small quantity of combustion gases, referred to as blow-by, always flows past the piston ring and down into the crankcase of the engine. In order to prevent excessive overpressure, partially caused by the blow-by gases, from occurring in the crankcase, the crankcase must be ventilated. The more effective the ventilation is the lower the overpressure in the crankcase will be and, therefore, the lower the engine pumping losses will be.
In modern engines, closed crankcase ventilation minimizes environmental effects. Normally, the blow-by gases are led out from the crankcase via a hose to the inlet manifold of the engine before the throttle and mix with the intake air. In order to separate oil unavoidably mixed with blow-by out of the oil mist, different types of filters and oil traps are used in the crankcase ventilation. All previously known crankcase ventilation systems have not made it possible to minimize a certain overpressure in the crankcase that increases as power demand increases. This means that a much higher pressure exists in the crankcase of the engine than in the combustion chamber during the intake stroke. This crankcase pressure tends to press the oil mist in the crankcase past the oil scraper ring of the piston and into the combustion chamber of the engine. In order to minimize oil flow to the combustion chamber, the ring tension must be high for the oil scraper ring. The oil scraper ring is the one component that causes the greatest internal friction in the engine. The oil that nevertheless penetrates into the combustion chamber of the engine not only causes pollution in the engine exhaust gases, but also places strain on the catalytic converter. Further, it lowers the octane rating of the fuel, which in modern engines with knock sensors and automatic ignition advance leads to a retarding of the ignition and thus increased fuel consumption. Last but not least, the oil consumption of the engine itself and the cost of replacing used oil are directly dependent on how much oil penetrates into the combustion chamber because of the pressure difference between the crankcase and the cylinder space above the piston.
The present invention provides a piston that can both take up at least a portion of the volume of combusted and/or uncombusted air-fuel mixture which, during the combustion stroke, is pressed past the piston rings, and obtain a reduction in the pressure of the volume of combusted and/or uncombusted air-fuel mixture taken up in the piston. This is accomplished by arranging a collection chamber between the piston ring grooves. The collection chamber has a peripheral groove in the lateral surface and at least one space arranged in the piston that communicates with the collection chamber. The collection chamber and space collect uncombusted air-fuel mixture and combustion gases that have passed at least one of the piston rings.
The design according to the invention makes it possible to maintain substantially near equilibrium pressure between the combustion chamber and the crankcase. This means that an underpressure is present in the crankcase during the inlet stroke. The pressure difference over the piston rings becomes so negligible that ring tension in the oil scraping ring is reduced to a fraction of what is normal without the risk of oil penetration from the crankcase to the combustion chamber.
In addition to the direct effects that the pressure balancing gives in the shape of lower oil and fuel consumption, important secondary effects are attained. Lower ring tension, producing a lower internal friction with consequential lower fuel consumption, leads to lower starting power for the starting motor, i.e., smaller starting motor and starting battery. A smaller quantity of pollution in the exhaust gases caused by oil in the combustion chamber means a lower load on the catalytic converter, which can be made smaller. Finally, the need for external components such as heating arrangements for preventing blow-by from freezing, oil traps, and hoses with associated connection parts can be eliminated, leading to cost savings.
Unavoidably, a small quantity of blow-by, unburnt fuel and other pollutants that reach the crankcase cannot be ventilated out. This quantity remains as a suspension in the oil in the crankcase, contributing to an accelerated ageing process of the oil and impairing its lubricating qualities. This, in turn, influences the life span of the engine.
Preferably, the cylinder in which the piston is designed for reciprocating motion is provided with an evacuation channel oriented relative to the collection chamber so that, after a predetermined movement of the piston from its upper or lower dead point, a communication is established between the collection chamber and the evacuation channel. This channel, in turn advantageously communicates with an intake channel of the internal combustion engine.
In this manner, uncombusted air-fuel mixture and combustion gases are prevented from reaching the crankcase. Instead, they are ventilated directly into the evacuation channel and flow to the intake channel, since there is overpressure in the collection chamber while there is underpressure in the evacuation channel. Without this structure, uncombusted air-fuel mixture trapped beneath the first piston ring would flow back into the combustion chamber during the expansion stroke as soon as the cylinder pressure drops below the pressure of the mixture. However, this would occur too late for combustion of the mixture. By arranging a space in the piston that communicates with the collection chamber, a relatively large volume is created in the piston. This volume is so great that the pressure of the air-fuel mixture and the combustion gases drops in the collection chamber and in the space.